Fuel starvation - Cause of Breakdown

First a warning: In the event of a breakdown think road safety; have you got a hi-visibility jacket for yourself and passengers, if so wear it.  Can you place a warning triangle, or a person safely, back down the road, but make sure you collect the triangle and person afterwards.

You are stuck at the roadside because the engine has spluttered to a halt or just stopped.  What happens next?  These notes supplement the article Fuel System Explained

You have checked that a good spark appears at each plug and that you have adequate fuel in the tank, so it all points to a fuel starvation problem.  This article might help you to solve the problem methodically.

Remove the carburettor bowl:
1.    Is it full of petrol?  If so the problem is probably a blocked jet, so remove the float and fuel and blow the jets; replace the bowl, prime the carburettor and try to start the engine.

2.    Bowl has no petrol in it?  Then hold a rag a little way below the top of the carburettor and prime to see if any petrol comes through the valve.  If none, then make sure that the valve moves freely, remove it and also give it a blow to clear it as a precaution.  Whilst it is removed prime again to check if any fuel is coming through the pipe from the fuel pump.  If yes, then refit the carburettor and try to start the engine.

If the answer is none, then the problem is further down.

3.    First disconnect the pipe feed from the exit side of the pump and see if any fuel comes from the pump when it is primed.  Always catch the fuel in a rag.

4.    If there is no fuel coming through then the problem is now likely to be with the pump.  But before taking it apart do ensure that fuel is coming from the tank to the pump, by disconnecting the feed pipe and holding it down so that gravity should provide a trickle.

5.    If nothing then there may be a blockage in the pipe coming from the tank.  As you are, of course, carrying a reasonable length of fuel hose attach this to the pipe from the tank and blow until you, or someone, hears bubbles in the fuel tank.

If that is ok, then the problem is with the pump:

6.    Carefully dismantle the pump, catch the screws as they will always drop onto the road, and then try to find them on dark coloured tarmac!!!

7.    Is the diaphragm sound?  When you prime some fuel should appear; if not replace it with the spare that you are carrying.

8.    If the answer is still no fuel appearing, then suspect that sludge in the well of the pump is causing a blockage; dismantle and clean.

As you have now checked everything in the fuel system you can only put it all back together again, prime the carburettor and try to start the engine.

Regular maintenance:
Most problems in the fuel system can be avoided with regular maintenance; clean out the carburettor bowl and blow the jets, and if you have fitted a fuel filter clean that at the same time, when you are doing other servicing on your 'Seven' every few months.  It will save a lot of aggro at the roadside. 

Remember; when you breakdown you could be miles from anywhere, with no mobile phone signal and it might be raining!!   Also remember that if you carry the spares you are unlikely to need them; you will often only need them when you haven't got them - that's life.

NB. Always be aware of the problem with stale fuel.  If you do not use your car regularly and are not refilling the tank with new petrol then fine microbial threads can form relatively quickly in the tank and block the fuel system at several places.